As the information society develops, the demand for display devices is increasing in various forms. In recent years, various display devices such as a liquid crystal display device (LCD), a plasma display panel (PDP), an electro luminescent display (ELD), and a vacuum fluorescent display (VFD) have been studied and used.
Among these, a display device using an organic light emitting diode (OLED) has an advantage of being excellent in luminance characteristics and viewing angle characteristics compared to a liquid crystal display device, and very thin owing to lack of a backlight unit.